A parallel plate capacitor with width 4 cm, length 8 cm and separation between the plates of 4 mm is connected to a battery of 20 V. A dielectric slab of dielectric constant 5 having length 1 cm, width 4 cm and thickness 4 mm is inserted between the plates of parallel plate capacitor. The electrostatic energy of this system will be _______ ε0 J. (Where ε0 is the permittivity of free space).
Correct Answer: 240
Solution and Explanation
The correct answer is 240
\(d_1 = 4×10^{-3}\)
\(A_1 = 8×4×10^{-4}m^2\)
V = 20V
\(d_2 = 4×10^{-3},\)
\(A_2 = 4×1×10^{-4}m^2\)
\(C_{eq} =\frac{(A_1+5A_2-A_2)_{ε_0}}{d} = \frac{3(16)×10^{-4}}{4×10^{-3}}ε_0\)
\(ε = \frac{1}{2} C_{eq}V^2 \)
\(= \frac{3}{2}(\frac{4}{10})(400)ε_0 = 240ε_0\)
Therefore , the electrostatic energy of this system will be 240 ε0 J
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Concepts Used:
Electrostatic Potential and Capacitance
Electrostatic Potential
The potential of a point is defined as the work done per unit charge that results in bringing a charge from infinity to a certain point.
Some major things that we should know about electric potential:
- They are denoted by V and are a scalar quantity.
- It is measured in volts.
Capacitance
The ability of a capacitor of holding the energy in form of an electric charge is defined as capacitance. Similarly, we can also say that capacitance is the storing ability of capacitors, and the unit in which they are measured is “farads”.
Read More: Electrostatic Potential and Capacitance
The capacitor is in Series and in Parallel as defined below;
In Series
Both the Capacitors C1 and C2 can easily get connected in series. When the capacitors are connected in series then the total capacitance that is Ctotal is less than any one of the capacitor’s capacitance.
In Parallel
Both Capacitor C1 and C2 are connected in parallel. When the capacitors are connected parallelly then the total capacitance that is Ctotal is any one of the capacitor’s capacitance.